Sheet feeding apparatus

ABSTRACT

A sheet feeding apparatus comprises a loop transport belt defining numerous air passage holes, which are stretched and hung above the recording sheet so that an outer surface of the belt faces to a top surface of the recording sheet and driven to go around; a suction device that depressurizes and sucks air through the air passage holes of the transport belt, causing the recording sheet to adhere to the outer surface of the transport belt; and a corrugator that protrudes beneath the surface of the transport and pushes the recording sheet down, and retracts above the surface of the transport belt, and is installed beside and adjacent to the transport belt in a width direction of the recording sheet, wherein a position where the corrugator contacts with the recording sheet can move between a position where the corrugator protrudes and a position where the corrugator retracts.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet feeder that draws and feeds a recording sheet one by one from a stack of recording sheets of a given size housed in image forming or printing equipment such as printers and copiers.

2. Description of the Related Art

Image forming or printing equipment of electrophotographic, ink jet, and other types is equipped with a sheet housing in which a stack of recording sheets cut to a given size is housed. When image formation or printing is performed, a recording sheet is drawn and fed one by one sequentially from the top of the stack. At this time, in order not to feed two ore more sheets that cling together as they are, a mechanism to prevent feeding of sheets that cling together is used.

Several types of sheet feeders that are able to feed recording sheets one by one, preventing feeding of sheets that cling together, have been proposed. As one of these types, there exists a sheet feeder that draws up a recording sheet by air depressurization and suction, thereby separates the sheet from other recording sheets, and feeds the sheet. Sheet feeders of this type are previously described.

These sheet feeders include loop transport belt defining numerous air passage holes, which are tightly stretched and hung in a position to face the top surface of a stack of recording sheets stacked in a sheet housing, a suction device that depressurizes and sucks air through the air passage holes of the transport belt from inside the belts, a drive device that revolves the outer surfaces of the transport belt, and an air blow device that blows air onto an edge of a recording sheet being transported from underneath, forward in the sheet transport direction. A plurality of the transport belts can be set parallel, stretched and hung and driving the belts is controlled so that the belts go around in the same direction at a constant speed.

In such a sheet feeder, air is depressurized and sucked by the suction device from inside the transport belt through the air passage holes of the belts. By this air suction, a top sheet in the stack of recording sheets is drawn and adheres to the outer surfaces of the transport belt. At this time, a recording sheet adheres to the surfaces of the plural belts, which makes a wavy corrugation in the recording sheet. Even if two or more recording sheets that cling together are drawn and adhere to the surfaces of the belts, by an elastic restoring force or the like of the deformed sheets, a lower sheet or sheets are separated from the top sheet. Thus, only the top sheet adheres to the transport belt and is fed to a transport path by the revolving transport belt. On the transport path, a pair of transport rollers is provided to nip a recording sheet from both sides. When the forward edge of a sheet is nipped by the transport roller pair, the sheet is transported by the revolving roller pair to a position where image formation takes place on the sheet.

This sheet feeder needs the suction device and the structure of the sheet feeder becomes somewhat complex. However, even if the sheet feeder feeds recording sheets at high speed, feeding of sheets that cling together occurs little. This sheet feeder is often adopted in high-speed printing or image forming equipment.

The above sheet feeder that feeds a recording sheet, separating it from other sheets by air depressurization and suction has the following problem and should be improved in this respect.

In image forming or printing equipment, generally, a variety of recording sheets are used, involving thick paper, thin paper, paper with high bending stiffness, and soft paper. When these kinds of recording sheets are drawn to adhere to the above transport belt by air depressurization and suction, the condition of a corrugation occurring in a recording sheet differs among paper kinds. To prevent feeding of sheets that cling together, it is easy to separate second and subsequent sheets from the top sheet for some kinds of paper, whereas it is difficult for other kinds of paper. If these different kinds of paper are drawn to adhere to the transport belt in all the same manner, in the case of paper with high permeability to air and soft paper, feeding of sheets that cling together are liable to occur, unless the sheets are deformed to a great degree. On the other hand, in the case of thick paper and very stiff paper, it is difficult that a sheet is drawn to adhere to the transport belt and transport failure is liable to occur.

Meanwhile, when a recording sheet adhered to the transport belt is corrugated forcedly and fed as is onto the transport path, the deformed wavy sheet may enter a curve section of the transport path. If the stiffness of the recording sheet becomes large by being deformed into the wavy shape, the sheet may be bent forcedly by a transport guide in the curve section and locally folded, and its surface may be damaged. A defect occurs in an image formed on the sheet with such a damaged surface.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances and provides a sheet feeding apparatus.

To address the above-mentioned problem, according to an aspect of the invention, the present invention provides a sheet feeding apparatus that draws and feeds a recording sheet from a sheet tray, the sheet feeding apparatus comprises a loop transport belt defining numerous air passage holes, which are stretched and hung above the recording sheet so that an outer surface of the belt faces to a top surface of the recording sheet and driven to go around, a suction device that depressurizes and sucks air through the air passage holes of the transport belt, causing the recording sheet to adhere to the outer surface of the transport belt, and a corrugator that protrudes beneath the surface of the transport belt to which the recording sheet adheres and pushes the recording sheet down, and the corrugator retracts above the surface of the transport belt to which the recording sheet adheres, the corrugator is installed beside and adjacent to the transport belt in a width direction of the recording sheet, wherein a position where the corrugator contacts with the recording sheet can move between a position where the corrugator protrudes beneath the surface of the transfer belt to which the recording sheet adheres and a position where the corrugator retracts above the surface of the transfer belt to which the recording sheet adheres.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the present invention will be more apparent from the following description of the drawings, wherein:

FIG. 1 is a simplified cross-sectional view of a sheet feeding apparatus which is an embodiment of the present invention to show the apparatus structure;

FIG. 2 is a simplified front view of the sheet feeding apparatus shown in FIG. 1;

FIG. 3 is a sectional view on line A-A in FIG. 1 and FIG. 2;

FIGS. 4A and 4B are enlarged views of a corrugator used in the sheet feeding apparatus of FIG. 1 to show the corrugator structure and operation;

FIGS. 5A and 5B are simplified front views of the sheet feeding apparatus of FIG. 1 to show how a recording sheet is handled and transported by the apparatus; and

FIGS. 6A and 6B are simplified front views of the sheet feeding apparatus of FIG. 1 to show how a recording sheet is handled and transported by the apparatus.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will be described hereinafter, based on the drawings.

FIG. 1 is a simplified cross-sectional view of a sheet feeding apparatus which is an embodiment of the present invention to show its structure. FIG. 2 is a simplified front view of this sheet feeding apparatus. FIG. 3 is a sectional view on line A-A in FIG. 1 and FIG. 2.

This sheet feeding apparatus is equipped with a sheet tray 1 in which a stack of recording sheets 12 cut to a given size is housed, loop transport belt 2 defining numerous air passage holes throughout the dimensions of the belts, which are tightly stretched and hung in a position to face the top surface of the stack of recording sheets 12 stacked in the sheet tray 1, a suction device 3 that depressurizes and sucks air through the air passage holes 21 of the transport belt 2, a drive device 4 that drives the transport belt 2 so that the outer surfaces of the belts move around, corrugator 5 installed in positions adjacent to the transport belt 2 and supported to protrude beneath the lower outer surfaces of the transport belt 2 facing the recording sheets 12, and an air blow device 6 that blows air onto an edge of a recoding sheet 12 from underneath one side of the sheet tray 1 from which a recording sheet 12 is let out.

The sheet tray 1 houses recording sheets 12 stacked on a bottom plate 11 and the height of the bottom plate 11 is adjusted so that the top of the stack of recording sheets 12 remains at approximately the same height even if the quantity of recording sheets 12 loaded varies.

As is shown in FIG. 2 or FIG. 3, the transport belt 2 are four identical ones that are tightly stretched and hung in parallel by two rollers 41, 42 and supported so that their outer surfaces face the top surface of the stack of recording sheets 12 in the sheet tray 1 from above with a given gap between adjacent belts. The transport belt 2 are made of synthetic rubber and the outer surfaces are made to have large friction with a recording sheet 12. Throughout the dimensions of the belts, the air passage holes are substantially evenly distributed.

The drive device 4 drives to rotate one or both of the rollers 41, 42 by which the transport belt 2 are tightly stretched and hung and drives to move the outer surfaces of the transport belt 2 in the position to face a recording sheets 12 toward a direction of transporting the recording sheet.

The suction device 3 includes a duct 31 laid inside the transport belt 2 and a suction fan 32 which sucks air from the duct 31 and depressurizes the duct 31. The duct 31 is laid such that it contacts the transport belt 2 in the rear sides of the regions of the transport belt 2 facing a recording sheet and plural suction openings (not shown) are formed in the contact regions to become continuous with the air passage holes 21 provided in the transport belt 2. Thus, when the air in the duct 31 is sucked and depressurized by the suction fan 32, external air is sucked through the suction openings and the air passage holes 21 of the transport belt 2 and the recording sheet 12 being in an opposite position to the belts is drawn to adhere to the outer surfaces of the transport belt 2.

As is shown in FIG. 2, each of the corrugator 5 is placed between adjacent ones of the four transports belts 2 disposed in parallel. Each corrugator is mainly composed of a sheet contact member 51 supported such that it can move forward and backward between a position of protrusion beneath the transport belt 2 surface facing a recording sheet 12 and a position of retraction from the outer surface of the transport belt 2, an actuating rod 52 connected to the sheet contact member 51 to move the sheet contact member, and a solenoid 53 to drive the actuating rod 52.

The sheet contact member 51 is a long member in the direction of revolution of the transport belt 2. As is shown in FIG. 4A, one end of the sheet contact member 51 is supported rotatably on a support axis 54 and the other end is coupled to the actuating rod 52 in a mutually rotatable manner. By upward and downward motions of the actuating rod 52, as is shown in FIG. 4B, the end coupled to the actuating rod 52 moves upward and downward and the member turns on the support axis 54. The upper end of the actuating rod 52 is connected to the solenoid 53 and the actuating rod 52 is moved upward and downward by the operation of the solenoid 53. Thereby, the moderately curved bottom surface of the sheet contact member 51 is moved to the position of protrusion beneath the surface of the transport belt 2 facing a recording sheet 12 or the position of retraction from the transport belt 2 surface and is supported in that position.

The air blow device 6 discharges an air flow from a nozzle tip and blows the air flow into a limited area. The air blow device 6 is installed under the forward end of the sheet tray, that is, under a sheet transport path 7 onto which a recording sheet 12 is fed, and blows an air flow onto an edge of a recording sheet 12 adhered to the outer surfaces of the transport belt 2, drawn from the sheet tray 1. The air blow device 6 blows an air flow onto the edge of a recording sheet between the positions of the corrugator 5 installed in the width direction of recording sheets 12. When two or more recording sheets 12 clinging together are adhered to the transport belt 2, this air flow is blown between these sheets and it functions to facilitate the separation of second and subsequent sheets from the first sheet.

Next, how the sheet feeding apparatus operates is described.

In time with feeding a recording sheet 12, the transport belt 2 and the suction fan 32 of the suction device 3 are driven. By this suction, air inside the duct 31 is depressurized and air in the space between the outer surfaces of the transport belt 2 and the top surface of the stack of recording sheets 12 is sucked through the air passage holes 21 of the transport belt 2. A top recording sheet 12 in the stack is drawn to adhere to the outer surfaces of the transport belt 2. The transport belt 2 are revolved in the direction indicated by the arrows in FIG. 1, that is, the direction of feeding the recording sheet 12. The recording sheet 12 adhered to the belts is fed onto the sheet transport path 7.

When the recording sheet 12 is drawn by suction and adheres to the transport belt 2, all the sheet contact members 51 of the corrugator 5 protrude beneath the outer surfaces of the transport belt 2, as is shown in FIGS. 5A and 5B. The sheet contact members 51 contact the recording sheet 12 adhered to the outer surfaces of the transport belt 2 and impede the recording sheet 12 portions brought in contact with the members from touching the transport belt. Thereby, the recording sheet 12 deformed into a wavy shape is adhered to the belts, as is shown in FIG. 5A. At this time, if two or more recording sheets 12 that cling together are drawn by suction, as is shown in FIG. 5B, the suction force is exerted on the recording sheets 12 a, 12 b, but the suction force exerted on the lower sheet 12 b becomes smaller than that exerted on the upper sheet 12 a. Consequently, by the stiffness of the recording sheets, that is, elastic restoring properties of the sheets from deformation when they are deformed, clearances take place between the upper sheet 12 a and the lower sheet 12 b, as is shown in FIG. 5B. Also, wavy deformation causes a lateral slip between the contacted recording sheets in lamination. This makes it easier to separate the sheets. Then, an air flow from the air blow device 6 is blown into the clearances made between the recording sheets 12 a, 12 b. This air flow functions as a so-called air knife and facilitates the separation between the recording sheets that cling together. In this way, the lower sheet 12 b is separated from the upper one and drops in the sheet tray 1 and the only the top recording sheet 12 a adheres to the transport belt 2 and is fed onto the sheet transport path 7. Therefore, even for thin recording sheets and sheets with high permeability, feeding of sheets that cling together is positively prevented.

On the other hand, when recording sheets which are thick, very stiff, and hard to bend are fed, if all the sheet contact members 51 of the corrugator 5 protrude, as is shown in FIG. 6B, wavy deformation takes place, but only to a small degree, in a recording sheet 13. When plural recording sheets that cling tighter are drawn by suction and adhere to the belts, the effect of separating a lower sheet or sheets from the top sheet decreases. Large clearances between the recording sheet 13 and the outer surfaces of the transport belt 2 take place in wider areas, which may cause a fear that the adhesion force becomes insufficient and transport failure occurs. To prevent this, the corrugator can be controlled such that, for example, as is shown in FIG. 6A, only the central sheet contact member 51 a protrudes, whereas two members 51 b, 51 c at both sides remain in the retraction positions from the outer surfaces of the transport belt 2. In this state, when the suction device 3 is driven and a sheet is drawn to adhere to the outer surfaces of the transport belt 2, the recording sheet 13 is moderately curved, as is shown in FIG. 6A. Even if two or more sheets are drawn by suction, a lower recording sheet or sheets are separated from the top sheet and the top sheet contacting or nearly contacting the outer surfaces of the transport belt 2 is transported positively.

The recording sheets 12, 13 which are transported as above are fed onto the sheet transport path 7. When the forward end of a sheet is pinched by transport rollers 8, the rotating transport rollers 8 further transports the sheet along the sheet transport path 7 toward an image forming section. The corrugator can be controlled such that the sheet contact members 51 of the corrugator 5 retract from the outer surfaces of the transport belt 2 immediately before the forward end of the recording sheet 12 or 13 comes to the transport rollers 8 installed in a position nearest to the sheet tray. After the sheet is pinched by transport rollers 8, driving of the suction device 3 can be stopped.

Through the control as above, when being pinched by the transport rollers 8, the recording sheet 12 or 13 becomes almost planar, recovering from wavy deformation. Thus, even if the recording sheet 12 or 13 being moved by the transport rollers 8 is bent along a transport guide 9, the sheet will be free of local folds and surface damage. A trouble such as an unrecoverable crease is prevented from occurring when a corrugated sheet is pinched by the transport rollers 8.

While, in the above-described sheet feeding apparatus, the solenoid 53 is used to drive the sheet contact member 51 of each corrugator 5, a motor instead of the solenoid can be used. When the solenoid is used, it is difficult to control protrusion of the sheet contact member 51 so that the distance of protrusion can vary. However, by using the motor to drive the sheet contact member 51, the distance of protrusion of the sheet contact member 51 beneath the outer surfaces of the transport belt 2 may be adjusted appropriately according to the kind of recording sheets in use. Thus, when thin paper, soft paper, or paper with high permeability is used, the driving of the corrugator is controlled to increase the distance of protrusion of the sheet contact member 51. When thick paper or hard paper is used, the driving is controlled to decrease the distance of protrusion. Consequently, feeding of sheets that cling together may be prevented and good transportability can be achieved.

As described above, to address the above-noted problem, according to an aspect of the invention, the present invention provides a sheet feeding apparatus that draws and feeds a recording sheet from a sheet tray, the sheet feeding apparatus comprises a loop transport belt defining numerous air passage holes, which are stretched and hung above the recording sheet so that an outer surface of the belt faces to a top surface of the recording sheet and driven to go around, a suction device that depressurizes and sucks air through the air passage holes of the transport belt, causing the recording sheet to adhere to the outer surface of the transport belt, and a corrugator that protrudes beneath the surface of the transport belt to which the recording sheet adheres and pushes the recording sheet down, and the corrugator retracts above the surface of the transport belt to which the recording sheet adheres, the corrugator is installed beside and adjacent to the transport belt in a width direction of the recording sheet, wherein a position where the corrugator contacts with the recording sheet can move between a position where the corrugator protrudes beneath the surface of the transfer belt to which the recording sheet adheres and a position where the corrugator retracts above the surface of the transfer belt to which the recording sheet adheres.

In the above sheet feeding apparatus, when a recording sheet is drawn to adhere to the outer surfaces of the loop transport belt by air depressurization and suction, portions of the sheet are pushed out by the corrugator protruding the outer surfaces of the transport belt and other portions of the sheet contact the outer surfaces of the transport belt by suction, and thus the sheet may be positively deformed into a wavy shape. At this time, if two ore more sheets that cling together are drawn to adhere to the belts, the elastic restoring force from wavy deformation is exerted on second and subsequent sheets. By this force, the second and subsequent sheets are separated from the top recording sheet and only the one top sheet remains adhering to the transport belt. Thus, feeding of recording sheets that cling together may be prevented positively.

According to the kind of recording sheets in use involving the thickness, paper quality, size, etc. of sheets, putting the corrugator into the protrusion state beneath the surfaces of the transport belt facing the recording sheets or the retraction state can be selected and the sheets may be deformed according to the kind of recording sheets.

After the start of transporting a recording sheet adhered to the revolving transport belt, when an appropriate period of time has elapsed, the corrugator can be retracted. After the corrugator retract, the wavy deformation of the recording sheet adhered to the belts is relaxed and the sheet may be transported smoothly along a guide member of the transport path.

According to another aspect of the invention, in the sheet feeding apparatus, the transport belt may feed a recording sheet to a sheet transport path on which a transport roller is installed, and the corrugator retracts above the surface of the transport belt to which the recording sheet adheres before the recording sheet comes to the transport roller.

In this apparatus, the corrugator retract and the recording sheet that becomes almost free of wavy deformation comes to the transport rollers. Thus, the transport rollers pinch and transport the recording sheet that is almost planar. Even if the sheet transport path has a curve with large curvature, the recording sheet may move smoothly and such a trouble may be avoided that the recording sheet is creased or a paper jam occurs.

According to yet another aspect of the invention, in the sheet feeding apparatus, the plurality of the corrugators may be installed in the width direction of the recording sheet, and a part of the corrugators protrude beneath the surface of the transport belt to which the recording sheet adheres when the suction device is driven, and the remaining corrugators retract above the surface of the transport belt to which the recording sheet adheres according to the kind of the recording sheet in the sheet tray.

In this apparatus, by putting all the plural corrugator in the protrusion state beneath the outer surfaces of the transport belt, the recording sheet is deformed to large curvature and to a shape with some ridges. Thus, even for thin paper, soft paper, or paper with high permeability, feeding of sheets that cling together may be prevented with a high probability. On the other hand, by making one or some of the plural corrugator disposed in the width direction of the recording sheet protrude, the recording sheet is deformed moderately, thick paper or very rigid paper is made to contact or nearly contact with the transport belt and transported positively in wide areas, and feeding of sheets that cling together may be prevented effectively.

According to a further aspect of the invention, in the sheet feeding apparatus, a distance of protrusion of the corrugator varies according to the kind of the recording sheet in the sheet tray.

In this apparatus, by adjusting the distance of protrusion of the corrugator beneath the surfaces of transport belt facing the recording sheet, the distance of deformation, or the height of a ridge when the recording sheet adhered to the belts is deformed may be adjusted. Thus, it may be feasible to prevent feeding of sheets that cling together and transport a sheet assuredly according to the kind of recording sheets in use.

According to a still further aspect of the invention, in the sheet feeding apparatus, a plurality of the corrugators are installed in the width direction of the recording sheet, the sheet feeding apparatus further comprises an air blow device that blows air onto an edge of the recording sheet adhered to the transport belt from downside of the sheet transport path and from forward end of the sheet tray in a direction that the recoding sheet is fed, and the air blow device blows air between a plurality of positions of protrusions of the corrugators.

When two or more recording sheets are drawn to adhere to the outer surfaces of the transport belt, by blowing air onto the forward edges of the sheets, the air is blown between the sheets and it facilitates the separation of second and subsequent sheets from the top sheet. When the recording sheets are deformed by the corrugator, clearances between the sheets that cling together are likely to occur between the plural positions of protrusions of the corrugators and, by blowing air between these positions, the air is blown into the clearances, making it easier to separate the recording sheets.

As described above, the corrugator installed beside the transport belt may move between the protrusion position beneath the outer surfaces of the transport belt and the retraction position. The corrugator make wavy deformation of the recording sheet adhered to the outer surfaces of the transport belt by air depressurization and suction, and the deformation may be controlled according to the kind of recoding sheets. Consequently, feeding of sheets that cling together may be prevented effectively adaptive to various kinds of recording sheets and each recording sheet may be transported and fed onto the sheet transport path positively. By retracting the corrugator at proper timing during transport of a recording sheet, the recording sheet adhered to the belts may recover from deformation, and feeding the sheet onto the sheet transport path and transporting it along the sheet transport path may be performed smoothly.

The present invention may be embodied in other specific forms without departing from its spirit or characteristics. The described embodiments are to be considered in all respects only as illustrated and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

The entire disclosure of Japanese Patent

Application No. 205-185576 filed on Jun. 24, 2005 including specification, claims, drawings and abstract is incorporated herein by reference in its entirety. 

1. A sheet feeding apparatus that draws and feeds a recording sheet from a sheet tray, the sheet feeding apparatus comprising: a loop transport belt defining numerous air passage holes, which are stretched and hung above the recording sheet so that an outer surface of the belt faces to a top surface of the recording sheet and driven to go around; a suction device that depressurizes and sucks air through the air passage holes of the transport belt, causing the recording sheet to adhere to the outer surface of the transport belt; and a corrugator that protrudes beneath the surface of the transport belt to which the recording sheet adheres and pushes the recording sheet down, and the corrugator retracts above the surface of the transport belt to which the recording sheet adheres, the corrugator is installed beside and adjacent to the transport belt in a width direction of the recording sheet, wherein a position where the corrugator contacts with the recording sheet can move between a position where the corrugator protrudes beneath the surface of the transfer belt to which the recording sheet adheres and a position where the corrugator retracts above the surface of the transfer belt to which the recording sheet adheres.
 2. The sheet feeding apparatus according to claim 1, wherein the transport belt feeds a recording sheet to a sheet transport path on which a transport roller is installed, and the corrugator retracts above the surface of the transport belt to which the recording sheet adheres before the recording sheet comes to the transport roller.
 3. The sheet feeding apparatus according to claim wherein a plurality of the corrugators are installed in the width direction of the recording sheet and a part of the corrugators protrude beneath the surface of the transport belt to which the recording sheet adheres when the suction device is driven, and the remaining corrugators retract above the surface of the transport belt to which the recording sheet adheres according to the kind of the recording sheet in the sheet tray.
 4. The sheet feeding apparatus according to claim 1, wherein a distance of protrusion of the corrugator varies according to the kind of the recording sheet in the sheet tray.
 5. The sheet feeding apparatus according to claim 1, wherein a plurality of the corrugators are installed in the width direction of the recording sheet, the sheet feeding apparatus further comprising an air blow device that blows air onto an edge of the recording sheet adhered to the transport belt from downside of the sheet transport path and from forward end of the sheet tray in a direction that the recoding sheet is fed, and the air blow device blows air between a plurality of positions of protrusions of the corrugators. 